Process of cracking hydrocarbon oils under pressure to produce a lowboiling-point fraction from a higher-boiling-point oil or fraction



Mar. 20, 1923.

PROCESS OF CRACKING HYDROCARBON OILS UNDER PRESSURE TO PRODUCE A LOW BOILING POINT R. W. HANNA ET AL.

FRACTION FROM A HIGHER BOILING POINT OIL OR FRACTION I'ILED AUG. 29, I921.

Patented Mar. 20, 19233 iaeaaze UNITED STATES PATENT @FIFEQE.

RICHARD "W. HANNA, WILLIAM D. MASON, AND WALTER G. HAMILTON, OF RICH- MOND, CALIFORNIA, ASSIGNORS TO STANDARD OIL COMPANY, OF SAN FRANCISCO, CALIFORNIA, A CORPORATION OF CALIFORNIA.

PROCESS OF CRACKING HYDROCARBON OILS UNDER PRESSURE TO PRODUCE A LOW- BOILING-POINT FRACTION FROM A HIGHER-BOILING-POINT OIL OR FRACTION.

Application filed August 29, 1921. Serial No. 496,403.

To all-whom it may concern:

Be it known that we, RICHARD \V. HANNA, WILLIAM D. MAsoN, and \"ALTER G. HAMIL- rox, citizens of the United States of America', residing at Richmond, Contra Costa County,- State of California. have invented a new-and useful Process of Cracking Hydrocarbon Oils Under Pressure to Produce a Low-Boiling-Point Fraction from a Highe-r-Boiling-Point Oil or Fraction, of which the following is a specification.

This invention relates to the art of cracking hydrocarbon oils under pressure to produce a low boiling point fraction from a higher boiling point oil or fraction.

In the cracking, under pressure, of a high boiling point oil or distillate to produce na-phthaor other low boiling point fraction, it has been the common )ractice to charge the oil to be cracked into t e still or cracking system, cold, (i. e., at normal temperature or slightly heated) and then bring the entire charge up to the temperature and pressure of the required cracking operation. In some adaptations of such process, some additional charging stock or oil to be cracked has been fed into the apparatus by feeding the same either into the vapor line, reflux apparatus, or directly into the still or system. This additional charging stock has been vso introduced co-1d, i. e., either at normal temperature, or slightly heated by vapor heat exchangers as a fuel economy.-

The still or heating coil has been subjected to heat in degree and amount sufficient to raise the Whole body of oil to and maintain it at the cracking temperature. This has resulted in the heating element or unit being subjected to such a high degree and amount of heat as to cause very rapid deterioration of such heating element or unit, in order to heat all the oil to the temperature of the cracking operation. Portions of the oil have necessarily been abruptly subjected to much more intense heat than required in the cracking operation, thereby causing excessive c-racklng of portions of the oil and the production of excessive amounts of gas and heavy bodies, tar, carbon, etc.

Heretofore very material portions of the oil, (and in some processes all of the oil as it was subjected to the cracking operation, have been abruptly subjected to excessive raises in temperature causing excessive cracking resulting in the production of excessive amounts of gas and of heavy bodies, tar, carbon, etc., with a resultant loss in the yield of the desired low boiling point product and the production of large amounts of unsaturated hydrocarbons.

We propose to bring the entire body of the oil, to be subjected to the cracking operation, to the required cracking temperature without subjecting any portion thereof" to an abrupt or to an excessive raise in temperature thereby avoiding such excessive cracking and thereby subjecting all the oil to an even and uniform cracking distillation.

To this end we provide for a primary or preparatory heating of the charging stock before introducing it into the cracking unit or system. I

This primary heating is to such a temperature as will enable us to introduce the Oll at such temperature into the cracking unit or system and there raise it to and maintain it at the temperature of the cracking operation without the necessity at any time during the process of subjecting any part of the oil to either an excessive temperautre or to too abrupt raise in temperature.

Preferably such primary heating is given to the oil as it is being fed to the cracking apparatus or system. \Vhile such primary heating is preferably produced by raising the temperature of the oil as it progresses toward the cracking system evenly through the body of the oil; it is also preferable that such primary heating be affected in comparatively short time, and preferably immediately before passing the oil into the cracking temperature as thereby polymerization is decreased. Polymerization is to be avoided as far as possible as" the polymerized portions decompose most readily and break down to an excessive degree producing gas and heavy bodies, thus causing material losses in volume of yield, quality of yield,

' and excessive production of'hea-vy residual bodies.

This primary heating may be wholly or partially accomplished in various ways, as

for example, waste heats of the refinery (such as the heat from vapor heat exchangers, refluxing condenser apparatus, and the like,) may be utilized to partially raise the temperature of the charging stock and such partially heated charging stock then passed into a primary heater, in the form of a still or coil, directly or indirectly heated, wherein it may be raised to such desired temperature, or from such waste heat exchangers, etc., the charging stock may be conducted through heating devices arranged to be heated by the waste heat of stacks, finally conducted through such a primary heater, still or coil to bring such oil to such desired temperature. As this charging stock is necessarily a distillate, or mixture of distillates,

it will possess a materialrange of boiling points all relatively higher than the low boiling point product desired. We take a charging stock, therefore, with a material range of boiling points; to wit, of not less than 200 F., and in the primary heating keep such stock under such a pressure as to at all times during such primary heating prevent vaporization of any material portion.

. of the pressure maintained during the cracking operation is maintained on the charging stock during the primary heating. Vaporization of any material portion of the charging stock during primary heating is t-hereb prevented.

In t e preferred embodiment of our invention in a process of cracking under pressure we use a charging stock composed of the high boiling point oil or fraction to be cracked and a relatively lower boiling point distillate, fraction or oil, (termed by. us solvent oil,) which will be substantially unaffected at the temperature and pressure of the cracking operation and which is a higher boiling point oil than the product to be produced. This charging stock we subject to such rimary heating to bring the temperature t ereof to such an approximation of the temperature of the desired cracking operation that the additional heat ing required for the heat necessary for the decomposition and the resultant vaporization should not be so intense as to cause that portion of the charging stock which comes into contact with the metal surface of the heating element to be excessively decomposed. This primary heating may be to a temperature just below that of the temperature of the cracking operation so that the heat transfer from the heating element.

of the cracking system. proper to the primarily heated oil when introduced thereinto need not be greater than the heat necessary to supply the heat of the reaction, vaporization, refluxing and radiation losses; but such primary heating must be to a higher temperature than can be effected by utilizing the waste heat ofthe cracking operation, such as by vapor or residual oil heat exchangers, etc, and must therefore be secured by a source of heat supply extraneous to the main cracking system. If by such primary heating the charging stock is raised to a temperature of substantially 500 F. without material vaporization and introduced into the cracking system or unit at such temperature we have found that a much more even cracking operation can be maintained; that such incoming charging stock can be then raised to and maintained at the cracking temperature with much less danger of excessive cracking of any portion thereof; that the yield of the low boiling point vapor is increased; the capacity of the cracking unit or system increased; a greater rate of distillation may be maintained; and

the destructive action" upon the cracking apparatus or system may be materially decreased, and that the nearer such primary heating approximates the critical temperature of the cracking operation the more each of the benefits and advantages are increased.

As an example, an oil easily cracked such as heavy lubricating oil fractions of a California crude oil, distilled off under conditions of high vacuum, over a residuum producing a 70 penetration asphaltum, will show incipient cracking at a temperature of 500 F. and quite active decomposition at a temperature of 550 F. With fractions, of such characteristics it is undesirable to carry the primary heating to a temperature above 500 F'.

When our invention is to be embodied in a process of pressure distillation to produce a substantially uniform low boiling point fraction from a higher boiling point oil or fraction, inlthe preferred embodiment of our invention, we take the said charging-stock which has been so primarily heated and continuously circulate the same through a. closed system; maintaining in the system a substantially uniform temperature and pressure. providing means whereby such primarily-heated charging stock as it is introduced to the system shall be brought to the temperature of the system, continuously withdraw the low boiling point vapor as produced, and by dilution by constantly feeding into the system additional primarily heated charging stock and by discharge of the heavy bodies resultant from the cracking in solution with the solvent oil of the charging stock. keep a substantially conreflux condenser.

stant volume in the system and keep the circulating oil or menstrum from becoming sufficiently concentrated to cause deposition in the system.

While our invention is not dependentupon any particular form or construction of apparatus it may be more fully and readily comprehended in connection With a system and apparatus by which it may be performed. We have therefore shown and illustrated in the accompanying drawings a diagrammatic View of a system and apparatus in which a preferred embodiment of a process employing our invention may be performed. In such drawing 1 indicates a storage vessel for the high boiling point oil which is to be cracked, 2 a suitable pump designed to pump such oil from the storage 1 and force the same through a pipe or conduit 3. 12 indicates a storage vessel for the solvent oil which is to be mixed with the high boiling point oil to be cracked, for the purpose of taking into solution the heavy bodies produced by cracking such high boiling point oil and prevent such heavy bodies from being so reduced as to'c'ause deposition in the system. Such solvent oil may be any lower boiling point fraction of the same oil, of which the oil to be cracked is a part, or of any other oil provided, however, that such solvent oil shall be substantially unaffected at the pressure and temperature employed in the cracking of the particular oil operated upon. It is also understood that the preferred embodiment of our process is not limited to the use of any particular non-crackable or solvent oil either produced in the system or added from any outside source but may be merely a relatively low boiling point fraction ofthe oil,

cracking of the high boiling point fraction whereof is to be performed. 13 indicates a pump adapted to draw solvent oil through the pipe 14 from the vessel 12 and force it through a pipe or conduit 15 into the pipe or conduit 3 where it is mixed'with the oil to be cracked. It is obvious that mixing of the oil to be cracked and solvent oil may take place before the same are supplied to the storage or supply tanks or vessels of the systems in which case such'mixtures may be drawn directly from one tank or vessel and forced through a pipe or conduit 3. From the pipe or con duit 3 this charging stock is forced into and through a waste heat exchanger .4 at the condenser 18 and thence through a continuation of such pipe or conduit 3 through a heat exchanger 5-where such charging stock is subjected to the waste heat of the From such heat exchanger 5 the conduit 3 is preferablycarried to a waste heat exchanger6 at the discharge or Withdrawal of. the hot residual solution of the system. From this heat ex: changer 6 the charging stock is forced through a continuation of the conduit '3 into and through a heating coil 7. This heating coil may be of the ordinary or any preferred construction and fired or heated in any preferred manner. By means of this coil the charging stock is brought to the desired temperature for introduction into the cracking system. Such desired teinperature is necessarily higher than any temperature to which the charging stock could be raised by mere waste heat of vapor heat exchangers. From the heating unit or coil 7 a pipe or conduit 8 leads into the 30 heating coil of the cracking system. While wev prefer to introduce the primarily heated charging stock into such heating coil it may be introduced at any other desired point in the system.

The cracking apparatus or system proper ,is indicated as consisting of a suitable vais connected by means of a pipe or conduit 27 with the vaporizing chamber or evaporator 9. 28 represents the vapor line from the evaporator 9. 17 is a dephlegmator or reflux condensing apparatus in said line 28 and 18 is a condenser connected with said dephlegmator. 19 indicates a receiver connected with the condenser and 20 is a valve where pressure is released and the condensate delivered to storage. 21 is a discharge pipe from the evaporator 9. 22 is a cooler 11 to which the pipe 21 leads, through the waste heat exchanger 6. 23 is a discharge valve from the cooler and 24 is a receiver. The pump 2 affords a means by which any desired pressure may be placed and main tain ed upon the char ing stock as it is being primarily heated? The presence in the charging stock of a fraction of oil of lower boiling point than the oil to be cracked, which lower boiling point fraction is substantially unaffected at the temperature and pressure of the cracking operation, provides a medium by which the heavier bodies produced from the cracking of the oil may be carried in solution and pre-' vented from being reduced so heavy or so near totar or carbon as to cause deposition in the system. In other Words, this solyent oil immediately takes and holds in solution the relatively boiling point oil or This 95 fraction produced by the cracking, so that it may be discharged from the apparatus.

Upon the cracking of the crackable oil into tion in the system takes place as these higher boiling point fractions. heavy hydrocarbons tarry or carbonaceous bodies take the brunt of the heat and unless held in solution by the solvent oil become further reduced towards tar or carbon. The degree of concentration, (of the solvent oil and high boiling point fractions produced by the cracking of the craekable oil,) which may be permitted in the system without danger of deposition will, of course, depend upon the oils charged into the system as, for example, the carbon residue test should not exceed ten times that of the charged oils. This is merely an example and will vary with the oils.

In the cracking of certain petroleum distillates there may be produced from the operation suflicient. solvent or non-crackable oil of unsaturated form to keep the solid hydrocarbons, tarry residues or higher boiling point fractions in solution so that no deposit will form on the metal surface of the heated element, in which casev it is unnecessary to addia solvent or non-crackable oil from an outside source. A certain amount of noncrackable or solvent oil passes off with the solidhydrocarbons, tarry residues, or higher boiling point fractions in solution. This may be replaced from storage as needed.

As an example of the proportion of oil to be charged with a solvent oil, we add one volume of the former to as much as three or five volumes of the latter inthe system at any moment; and as an example of a desirable cracking pressure and temperature of the oil to be cracked we give 105 to 120 pounds absolute and 745 degrees to 800 degrees F., but it is to be understood that these proportions and the pressure and temperature may vary according to the oils used.

'By thus primarily heating the charging stock we are enabled to most materially reduce the heat demand. upon the heating element of the cracking system proper which, therefore, need not be greater than to supply the heat of the reaction, vaporization, refluxing and radiation losses thereby eliminating excessive cracking of portions of the oil, reducing essentially the quantity of fixed gas produced and the resultant quantities of higher boiling point fractions, tarry and carbonaceous residues, minimize the destructive action upon the heating element, increase the vaporizing capacity of the system, decrease the heat transfer per unit area of the cracking element required in the cracking operation proper and are enabled to produce a much-more uniform product of the desired low boiling point and atdecreased cost. Excessive cracking of a portion of the oil has a very detrimental effect on the quality of the low boiling point product as it results in the production of highly unsaturated hydrocarbons, and by avoiding such excessive cracking we are thus enabled to produce a better and more valuable product.

It is thus seen that the primary heating of our invention comprehends the reduction of the heat demand upon the heating element of the cracking system proper to the end that the amount'of heat to be supplied to the oil by such heating element shall be reduced to approximately a minimum, and that the total heat demand of the cracking operation shall be divided'up so that the demand upon any given heating element shall not be sufiiciently, great to require an excessive heat transfer througn any such heating element to the oil. By eliminating the requirement of excessive heat transfer through the respective heating elements to the oil abruptk raises in temperature and excessive crac ing of portions of the oil may be substantially avoided. For example, with certain oils the following conditions have been noted:

We have found that forty per cent of the heat required to be supplied to the oil is to bring the oil .to the temperature of the cracking reaction and that approximately sixty per cent of the heat demand is to furnish the heat of the reaction, volatilization, refluxing, radiation losses, etc. Therefore, by supplying these independently of each other by separate and distinct sources of heat supply the demand of heat transfer can be so controlled that at no point in the operation or system must such a high temperature be supplied as to cause abrupt raise in temperature or excessive cracking.

As illustrative of one of the values of our subjecting the charging stock to such a pri mary heating beforeiit is introduced into the cracking system we have found that where the charging stock is so introduced at normal tempera-ture an external temperature of approximately 2600 F. is required upon the cracking element or coil; when so primarily heated to a temperature of 500 F. an external temperature upon the cracking unit or coil of approximately 2000 F.

is suflicient; with primary heating of the charging stock to 600 F. an external temperature on such cracking coil of 1800 F., and where the primary heating of the charging stock is carried to 700 "degrees F. an external temperature of 1000-1600 F., is suflicient. It will thus be seen that by such primary heating we are enabledto bring substantially the entire body of the oil beof petroleum oil having a material range of boiling points to a temperature above the boiling point of a fraction or fractions thereof while subjecting the same to a pressure suflicient to maintain the same in substantially liquid form, in which primary heating the oil is brought approximately to the active cracking reaction temperature ofthe higher boiling fractions of the oil, a

material portion of the heat necessary to raise the oil to such temperature being supplied by heating means independent of the heating means of the cracking system proper, then passing such heated liquid into a cracking system, which includes a heating zone, vaporizing chamber and condenser maintained under pressure, whereby the primarily heated oil is subjected to a higher temperature, the oil flowing through the heating zone being subjected in said heating zone to only such a degree of heat as will furnish the heat of reaction and offset heat losses from radiation, vaporization and reflux condensation, thereby through the medium of the aforesaid primary heating avoiding the exposure of any portion of the oil to excessive local temperatures and resultant excessive cracking and carbon deposit in any portion of the heating zone of the cracking system, and then passing the oil so heated in said heating zone to the evaporating chamber of the cracking sys tem. a

2. A continuous cracking process consisting in primarily heating a moving body of petroleum oil having a material range of boiling points to a temperature above the boiling point of a fraction or fractions thereof while subjecting the same to a pressure sufficient to maintain-the same in substantially liquid form, said pressure being in excess of the pressure of the cracking operation proper, in which rimary heating the oil is brought approxlmately to the active cracking reaction temperature of the higher boiling fractions of the oil, a material portion of the heat necessary to raise the oil to such temperature being supplied by heating means independent of the heating means of the cracking system proper, then passing such heated liquid into a cracking system, which includes a heating zone, va porizing chamber and condenser maintained under pressure, whereby the primarily heated oil is subjected to a higher temperature,

radiation, vaporization and reflux condensation, thereby through the medium of the aforesaid primary heating avoiding the exposure of any portion of the oil to excessive local temperatures and resultant excessive cracking and carbon deposit in any portion of the heating zone of the cracking system, and then passing the oil so heated in said heating zone to the evaporating chamber of the cracking system. a 1 3. A continuous cracking process consisting in primarily heating a moving body of petroleum oil having a material range of boiling points to a temperature above the boiling point of a fraction or fractions thereof and not less than 500 F., while subjecting the same to a pressure sufiici'ent to maintain the same in substantially liquid form, in which primary heating the oil is brought approximately to the active cracking reaction temperature of the higher boilingfractions of the oil, a material. portion of the heat necessary to raise the oil to such temperature being supplied by heating means independent of the heating means of the cracking system proper, then passing such heated liquid into a cracking system, which includes a heating zone, vaporizing chamber and condenser maintained under pressure, whereby the primarily heated oil is subjected to a higher --temperature, the oil flowing through the heating zone being subjected in said heating zone to only such a degree of heat as will furnish the heat of reaction and offset heat losses from radiation, vaporization and reflux condensation, thereby through the medium of the aforesaid primary heating avoiding the exposure of any portion of the oilto excessive local temperatures and resultant excessive cracking and carbon deposit in any portion of the heating zone of the crackin system, and then passing the oil so heated in said heating zone to the evaporating chamber of the cracking system.

ITThe continuous process of cracking which consists in primarily heating a mov ing body of petroleum oil having a material range of boiling points to a temperature above the boiling pointof a fraction or fractions thereof while subjecting the same to a ressure sufficient to maintain the same in substantially liquid form, in which primary heating, a material portion of the sensible heat necessary to raise the oil to the cracking temperature is supplied by means including a heat supply independent of the heat supply of the crackingsystem proper, and in which primary heating the oil is brought approximately to the temperature of the,

active cracking reaction of the higher boillUlD ing point portions of the oil, passing suchprimarily heated stock into a cracking sys-' tem, which includes a heating zone, a vaporizing chamber and condensing equipof therein is substantially avoided, continu-' ously. Withdrawing the low boiling point vapor as produced, continuously discharging from he system high boiling point products 0 such cracking, and continuously feeding into the said system additional primarily heated charging stock.

5. The process of cracking ahydrocarbon distillate to produce a substantially uniform low boiling point oil which consists in primarily heating a moving body of petroleum above the boiling point of a fraction or fractions thereof while subjecting the same to a pressure suflicient to maintain the same in substantially liquid form, in which primary heating a material portion of the sensible heat necessary to raise the oil to the cracking temperature is supplied by means including a heat supply independent of the heat supply of the cracking system proper, and 111 which rimary heating the oil is brought approximately to the temperature of the active cracking reaction of the higher 1,4aa22c pressure of the cracking operation, and then r passing such primarily heated oil into a cracking system which includes a heating zone, a vaporizing chamber, and condensing equipment, and wherein it is continuously circulated at a substantially constant pressure and temperature and in.the heating zone of which only the necessary heat is furnished thereto to supply the heat of reaction, and to offset heat losses from vaporization, refluxing and radiation, and from which heating zone such oil is passed to the evaporating chamber, whereby by such primary heating the subjection of any portion of the oil to excessive local temperature in the heating zone or excessive cracking of any portion thereof therein is substantially avoided, and whereby such high boiling point oil is cracked, continuously withdrawing the low boiling point vapor as produced, continuously discharging from the system high boiling point products of such cracking in solution, and continuously feeding into said system such primarily heated oil to maintain a substantially constant volume therein.

Signed at'Richmond, California, this 12th day of August, 1921.

RICHARD W. HANNAQ WILLIAM D. MASON.

"WALTER G. HAMILTON. -Witnesses:

' FREDERICK, S. LYON,

C. GREEN. 

